Could some-one please help. I have been stuck on this part for nearly 3 weeks and still have not gotten any further. :cryvaultboy: It's the part where the information is being leaked and some-one said that they had saw a person going into the control tower late at night i have tried waiting all night out of sight outside and inside somebody help me.

Wait some more, I had trouble catching him too. Try waiting.

That's not the thief. That guy enters the tower at 1am, however you need to progress further before he appears there. I think you need to talk to Colonel Hsu. When you go into the big building from the front, he's to the left on the ground floor in his own room.
I think you need to be in with the NCR to be allowed to help, though I'm not certain...sorry I can't remember more. But I'm fairly certain the person won't be there until you've notified Hsu of the suspicious activity.

@Hugga- that only gets the thing blown up. You need to overhear the spy, wait until it says to save the thing, then run straight to the thing and remove the bomb. Notifying anyone will doom the monorail.

Dont wait in the tower. Wait hidden behind one of the airplanes and sneak in behind him. If you try hiding inside the tower where the marker points to, he will never show up. Leave any companions inside the McCarren building.